Two new formulations of bioactive glasses were used as coatings on titanium alloy (TiAl6V4) implants for prosthetic applications in the orthopaedic field. The biocompatibility of these bioglasses, as well as their osteoconductive properties, were assessed by employing primary cultures of human osteoblasts. A nonbioactive glass, the titanium alloy and polystyrene surface were used as controls. The results obtained demonstrated that the two bioglasses elicited a rapid and strong proliferative response by osteoblasts, which spread, formed a close layer and then expressed the specific osteoblastic marker i.e. osteocalcin. In comparison, cells grew on the nonbioactive glass to a much minor extent, similar to that of polystyrene control, showing individual cellular elements not forming a compact sheet, but expressed levels of osteocalcin clearly higher than both the polystyrene control and the two bioglasses. Finally, a very low proliferative rate of osteoblasts and the synthesis of hardly detectable osteocalcin amounts were observed with the titanium alloy. In conclusion, our studies indicate that the new bioactive glasses are effective in stimulating osteoblast growth and differentiation.